The field of the invention is light beam deflection by using a periodically moving element and the present invention is concerned with a method and apparatus for displaying moving objects (targets) whereby two time-shifted object signatures are imaged in dot-grid manner on a detector.
In displays of this kind, the objects are imaged in the optical or infrared wavelength range on the detector and the attempt is made to detect also small angular objects far away.
The state of the art of these displays may be ascertained by reference to U.S. Pat. Nos. 4,266,847; 4,574,197; 4,588,254 and 4,733,072, the disclosures of which are incorporated herein by reference.
In the present state of the art these displays are implemented by carrying out parallel horizontal scanning in all directions or over a large sector in one or more superposed strips of a many element array. By comparing two time-sequential scans, the moving object may be recognized. In such methodology, however, this comparison requires an enormous memory. Moreover the repeat rate in such procedures is in the seconds range. During that time period of seconds the object (target), when moving at so low an angular speed as to be still significant, may have moved by so many image dots, that it will be difficult to unambiguously allocate the information of the two images.
Angular speed herein means the speed of lateral deviation of the moving object (target), for instance an incoming rocket, from the line of sight between observer and rocket. As a result, an object moving at high angular speed is of no interest because the object is passing by the observer, whereas the object will be more likely to strike the observer the less that angular speed. When this angular speed is null, the object is moving on a straight line directly toward the observer.